Magnetic transducer head



Allg- 1954 H. w. BAUMAN ETAL MAGNETIC TRANSDUCER HEAD I I I I I I I I r I I I f r i I 1 II Filed Jan. 16, 1952 lllllll Patented Aug. 17, 1954 l l r 2,686,846

UNITED STATES PATENT OFFICE V MAGNETIC TRANSDUCER HEAD Harold W. Bauman, Chicago, and Wesley L. Eddy,

Downers Grove, Ill., asslgnors to Ampro Corporation, Chicago, Ill., a corporation of Illinois Application January 16, 1952, Serial No. 266,767

3 Claims. (01. 1794002) This invention relates to magnetic transducer basic arrangement comprises a tubular shell of heads that are provided with dual transducing magnetically permeable material, provided at one gaps respectively for cooperation with different end with a transverse end wall that presents an record body track areas that pass the head with edge surface. A magnetically permeable core their longitudinal axis disposed in different par- 6 piece is disposed inside the shell and has a latallel planes that extend across the respective gaps eral surface portion parallel to, overlying and for registration of the respective track areas spaced from a portion of the end wall edge surwith the different gaps. A principal field of use face, whereby the opposed lateral and edge surof such a head is for recording or reproducing on face portions of the core piece and shell wall deor from the different ones of a pair of track areas 10 fine a nonmagnetic transducer gap and act as provided by a common tape-form record body. polar surfaces at its opposite ends. Inside the,

d more specifically, the arrangement is such shell, the core piece is encircled by an electrical that while the record body is driven in one direcwinding and beyond the winding from the gap tion transducing cooperation is maintained only the core piece is secured in close contactwith the between one track area and one gap while in the shell for magnetic circuit continuity. The faceother direction of record. travel only the other to-edge relation of the pole piece and shell end track area and the other head gap cooperate. wall surface portions defining the gap provides In the present invention the respective gaps for an easily accomplished practically parallel are provided by two different parallel branches relationbetween and registration of the gapof a magnetic circuit device having a single core defining polar surfaces, and also permits their structure that is linked with a single electrical spacing at any suitable distance to obtain a winding assembly. The gaps respectively are transducing gap of a desired length. Additionprovided by difierent ones of a pair of pole ally, the surface-to-edge relation provides a simpieces, each of which has a polar face that is ple way to produce a gap having a desired depth positioned in gap-defining relation to different of interface, the extent away from the record pole-providing surface portions of a common body path of the gap, since this gap dimension magnetic circuit element that is linked with the is fixed by the thickness of the wall providing electrical winding through the common core the edge surface that defines one side of the gap. structure. The different gaps are so relatively In the preferred transducer head arrangement positioned that the record body can be posi- 0 of the said application, the tubular shell is made tioned for cooperation of a selected one of its of a pair of half shell sections assembled in tracks with the corresponding one of the gaps matched relation, the end wall structure prowhile the second track is maintained sufficiently viding the gap-defining edge surface being an spaced from both gaps to preclude any transintegral part of one of the shell sections, and ducing effect between that second track and 5 therefore being accessible for finishing and poleither one of the gaps. l ishing to an accurately fiat, smooth condition.

Reference is made to the copending applica- The attachment of the core piece to the shell tion for United States patent of Harold W. Baupreferably is by a second face-to-edge relationman and Hugh A. Howell, Serial No. 266,767, ship between a rearward lateral surface portion filed January 16, 1952. That application disof the pole piece and a rear end wall edge surcloses and claims a type of assembly that is useful face portion. These second surface portions are in a variety of small, low power, electromagnetic maintained in close contact for substantial coninductance devices, in general, due to the extinuity of the magnetic circuit.

ceptional electromagnetic efiiciency of the elec- In the dual track transducer head disclosed and trical winding and magnetic circuit arrangement claimed in the above-identified application, each and the excellent magnetic characteristics proof a pair of pole pieces is assembled with the shell vi y the m n tic ir uit s ructur The in the indicated manner to provide a pair of arrangement particularly u u in magnetic transducer gaps that are suitably spaced for transducer heads b c the practical means respective cooperation with difierent record body provi d f r d mt n f a transducing p y tracks. Each pole piece is encircled by an indivery accurately finished and relatively positioned vidual winding, and each winding may be sepaspaced surfaces of the magnetic struc T rately energized to develop magnetic recording application in question discloses and claims both i fields across the gap defined by the pole piece single and multiple track transducer heads, and that it encircles, or by fields of a record track one specific form of the latter. In general, the traveling past that gap.

.side wall structure iii, rear end The present invention is directed to a shell type transducer head having the same type of electro magnetic, magnetic circuit, and gap-defining arrangements, but having a specifically different winding and core piece assembly, including gaps so relatively positioned as to permit either one of a pair of record track areas to be individually brought into cooperative relation with a corresponding one of the two gaps, while the other track area is maintained spaced away from both gaps. To provide this arrangement the gaps are spaced apart in directions extended transverse to the record body path, to register respectively with the different track areas, and they are also spaced apart in the general directions of record body travel to permit shiftable guide means to be selectively moved between two positions wherein respectively they are effective to so guide the record body tape that only one of its track areas ispresented to a gap for transducing cooperation with it.

In the accompanying drawings:

Fig. l is a somewhat schematic view, showing in plan a transducer head arranged according to the invention and indicating different paths which a record body may follow in its opposite travel directions, for cooperation in such directions respectively with different transducing gaps of the head.

Fig. 2 is a front end view of the head.

Fig. 3 is a section on line 3-3 of Fig. 2.

Fig. d is a section on line Q-l of Fig. 1.

Fig. 5 is a section on line 5-5 of Fig. 1.

Fig. 6 is a rear end view of the head.

The head comprises a shell having a tubular wall structure H and a front end wall structure l2 the outer surface of which provides contact portions for a tape form record body. The front end Wall structure i2 is bowed centrally outward in the general directions of the record path past it, such directions being indicated by the arrows it in Figs. 1 and 2. Front wall structure if is provided with an opening i i the opposite sides of which are defined by a pair of end wall edges l5, l6 spaced in the general directions of the record path, and preferably which are straight and flat. Edges l5, l6 respectively are spaced in the directions of the record path extent and oppositely from the center plane of the head, and thereby lie in regions of the bowed front wall surface that curve oppositely, laterally and rearwardly in the general directions of record travel. The surfaces of edges l5, iii preferably are disposed along planes that are substantially normal. to the curves of the front wall at the locations of such edges. A pair of pole piece members ll, l8 extend from inside the shell into opening i l, to provide lateral surface portions it, 2% that respectively overlie and are parallel to portions 2E, 72?; of the surfaces of the different edges i5, iii. Pole piece surface portions is, 2% are narrowly spaced from the different edge surface portions iii, if that they respectively overlie, at istances corresponding to a selected gap length. Such spacing advantageously is accomplished by bodies 23 of nonmagnetic material interposed between them, and for ease in assembly such bodies may be of strip form having inner portions bent to contact inner shell wall surfaces and adhesively secured to them, as suggested at Fig. 3. The pole piece members are relatively spaced in the directions of the lengths of edges iii to register with the different track. areas of a record body directed laterally over the surface of the shell end struc ture l3, and their end surfaces have widths in the directions of the lengths of edges l5, l5 correspondin to the widths of such track areas. The gaps 25, 25 defined between the pole piece lateral and shell wall edge surface portions l9, 2! and 2t, 22, thereby are of proper width for recording on or reproducing from such track areas. The pole pieces are of small. thickness as compared to their widths.

Pole pieces H, M are members of a common core structure, shown as comprising a pair of core pieces ill, 2? that are assembled in face to face, closely contacting registration and from which the different pole pieces respectively project in such formation as to provide the correct spacing and gap widths, and to provide parallelism between the surface portions i9, 26 and the edge portions 2!, 22 that they overlie. Core pieces 21, 25 together are encircled by a winding 29.

Selection of the particular gap 25 or 26 with which a record body is to cooperate may be provided for by record guide means movably mounted for shifting between positions wherein respectively they guide the record body to cooperative positional relation to one and the other of the gaps. Typical different record body paths are shown at 39 and 3! in Fig. 1. In each of these paths at the effective gap 25 or 25, the gap-defining surfaces are substantially normal to the record body surface facing the gap. As suggested by Fig. 1, the guide means may comprise a fixed guide device at each side of the head, shown as paired pins 32, and a pair of movably mounted guide devices, such as pins 33, 34, respectively lo cated to opposite sides of the head. Pins 33, 34 are reversely and selectively shiftable between active and inactive positions, pin 34 being shown in the former and pin 33 in the latter in full lines. The pin 33 or 34 that is in the active position, in cooperation with the fixed guide device 32 to the opposite side of the head, guides the record body in the path that places it in cooperative relation with the corresponding transducing gap 25 or 26. The fixed guide devices 32 serve to maintain the record out of cooperation with a gap 25 or 28 when the pin 33 or 34 corresponding to that gap is in its inactive position.

As has been suggested the common core structure of which pole pieces ll, l8 form members here provided by core pieces 21, 28, is secured in close contact with the shell beyond winding 29 from gaps 25, 25. Preferably the contact is accomplished by a closely contacting face-to-edge relation between a rearward lateral surface portion of each core piece El, 23 with edge surface portions of the shell rear end structure 12. In the specific arrangement shown in the drawings each half shell section has a rear end wall vportion 35 that provides a straight, flat edge 35. The different core pieces El, 23 have fiat lateral surface portions 3? that respectively overlie, are parallel to and closely contact the edges 35 of the different shell section rear end walls 35.

In accordance with one aspect of the invention set forth in the above-identified application, the inner turns of winding 29 closely surround and conform to the periphery of the core structure provided by pieces ill, preferably being wound on a thin walled tube 38 that is shaped to closely surround the core structure. The winding is confined at its ends by spool ends 39.

In assembling, the core and pole piece elements 21, ll and 28, G8 are secured together, the winding mounted on the core structure thus formed, and the shell sections assembled about the wind- The shell sections are securedtogether, as by soldering, and the core Advantageously the rear end wall edges 36 are inset with relation to side Wall edges 4| that permeable material of the record body that extends across the cooperating gap tends to magnetically short circuit the other gap, so that very little magnetic force is drained by the circuit branch that includes the inactive gap. In general, it may be said that the high efiiciency of We claim:

1. A dual magnetic transducer head comprising a core structure including a central common leg, a pair of pole pieces extended from said common leg, and a magnetic circuit leg struccircling said core structure.

3. A dual magnetic transducer head according to claim 2, wherein said front shell end wall substantially normal to the curve of said bowed Wall.

References Cited in the file of this patent UNITED STATES PATENTS Name Date Camras July 5, 1949 Porter Sept. 26, 1950 Number 

